The availability of all-silicon-based optoelectronic integrated circuit (OEIC) technology promises to revolutionize the optoelectronic industry and significantly impact a wide range of both military and commercial applications. One such area of impact is multi-chip module interconnectivity. Silicon-based OEICs will not only solve resistivity and high-capacitance problems by replacing electron transport with photons, they will also provide new functionality, such as circuit-level image processing. Silicon-based OEICs will also provide cost inroads to commercial markets as high-volume silicon processes enjoy economies of scale unparalleled by other electronic or optoelectronic materials technologies. Furthermore, silicon-based OEICs are expected to provide new functionality such as circuit-level image processing.
There are four technologies required to make silicon-based OEICs a reality: (1) detectors; (2) waveguides; (3) modulators and (4) emitters. While there has been considerable progress in the first three areas, a lack of an appropriate silicon-based light-emitting device, particularly a silicon-based laser, has greatly hindered the development of fully integrated silicon-based OEIC technology.
Most work to date on silicon-based OEICs has been based on III-V materials. However, post-ultra-large-scale integrated (ULSI) circuit work will likely continue to use silicon substrates because of low material costs, high mechanical strength, good thermal conductivity, and the highly developed processing methods available for silicon. One approach to integrating optical and digital electronics is to integrate III-V materials using epitaxially grown III-V layers for selected regions on silicon substrates. Although laser action from III-V layers grown epitaxially on silicon has been demonstrated, progress in this area has been limited by material quality problems resulting from the large lattice and thermal expansion mismatch between the two systems and incompatibilities between III-V material and silicon processing.
Reduced cavity size has been found to significantly affect laser characteristics for silicon-based lasers. When the cavity length is comparable to the wavelength of the cavity-defined radiation, cancellation of spontaneous emissions, zero-threshold lasing and enhanced gain may be achieved. The degree of gain enhancement is determined by the coherent length of the spontaneously emitted radiation. Gain enhancement has been predicted to increase more than five fold in III-V semiconductor microcavities as the emission linewidth decreases from 100 nm to 30 nm.
It has been shown possible to use certain thin films as a gain medium to produce high-intensity photoluminescence emissions. Nd-doped CaF.sub.2 thin films that function as gain mediums are described herein and specifically claimed in co-pending U.S. patent application Ser. No. (TI-16928). It, however, is highly desirable to achieve light emission from these films by electroluminescence rather by photoluminescence. By achieving light emissions through electroluminescence, electrons, instead of photons, produce amplified photons. This permits using optoelectronic devices made from these films by voltage control or variation. However, electroluminescence from CaF.sub.2 -hosted materials has been generally unsuccessful, because CaF.sub.2 has a wide bandgap material (12.1 eV) and, therefore, acts as a good insulator. Therefore, given poor electrical conductivity of these films, it is difficult to inject carriers into these films to excite the dopants.
As a result, there is a need for a method and apparatus that produces light emission from photoluminescence gain mediums such as CaF.sub.2 thin films using electroluminescence.
There is a further need for a method and apparatus for producing electroluminescence emissions for optoelectronic devices made of CaF.sub.2 thin films that permits voltage variation control of the opto-electronic devices.
Moreover, there is a need for a method and apparatus that permits carrier injection into CaF.sub.2 thin films to excite dopants for photoluminescence gain from the CaF.sub.2 thin films.